It has conventionally been known to granulate a polymer into particles and use the obtained particles as materials for, for example, pharmaceutical products and cosmetic products, or as products such as electrophotographic toners.
In a known method for granulating a polymer, a polymer is emulsified with an organic solvent (see PTL 1). According to this method, lactide, which is a ring-opening-polymerizable monomer, is ring-opening-polymerized to a polymer, which is then dissolved in methylene chloride serving as an organic solvent, neutralized with triethylamine, and after this, emulsified by phase-inversion emulsification with distilled water added dropwise and mixed therein. However, according to this method, methylene chloride remains in the particles. Therefore, the particles cannot be used for purposes in which any residual of the organic solvent is unwanted.
A known method for granulating a polymer without an organic solvent uses a compressible fluid (see PTL 2). According to this method, polyester is heated, melted, and then mixed with liquefied carbon dioxide prepared as a compressible fluid, and the resulting mixture is jetted from a nozzle so as to be granulated by depressurized expansion. In this case, if polymer components with high viscosities are locally present in the mixture, the nozzle might be clogged with them. Therefore, in the disclosed method, the polyester and the compressible fluid are mixed with a static mixer before jetting.